1. Technical Field
The invention relates to depositing a thin film in an organic electroluminescent (EL) device.
2. Discussion of Related Technologies
Organic electroluminescent (EL) devices that are self-emitting provide advantages in a plasma display panel (“PDP”) such as a wide viewing angle, high contrast, and fast response speed. As a result, they are considered to be the next generation flat panel display devices. Typically, organic EL devices include an anode, a cathode, and an organic layer having a light emission layer between the two electrodes. The organic layer is formed by way of deposition, as it is sensitive to humidity and cannot be formed in a general photolithography method.
FIG. 1 is an exploded perspective view of a conventional deposition mask frame assembly for depositing a thin film included in an organic EL device.
Referring to FIG. 1, the conventional mask 10 is formed of a metal thin plate 11 and includes a plurality of mask pattern units 12. The mask pattern units 12 enable fabrication of a plurality of unit devices including the organic EL devices onto a mother board (not shown). Each mask pattern unit 12 corresponds to a unit device. Each mask pattern unit 12 includes a plurality of openings 12a that correspond to the shape and pattern of the unit devices that will be deposited onto the mother board.
The mask 10 is fixed onto a frame 20 by applying tensile forces in an x direction and a y direction as denoted by the arrows in FIG. 1. The frame 20 includes left and right supporting bars 21, upper and lower supporting bars 22, and an opening 23.
When the mask 10 is fixed onto the frame 20, tensile force should be applied evenly to the mask 20, and a width of the openings 12a should be maintained within a predetermined tolerance.
The weight of a conventionally designed mask may cause it to droop even when the mask is fixed on the frame. A tensile force is applied to the mask in order to prevent the mask from drooping, which causes the left and right supporting bars 21 of the frame 20 to curve inward and the upper and lower supporting bars 22 to curve outward, as shown in FIG. 2. It is also possible that the left and right supporting bars 21 may curve outward and the upper and lower supporting bars 22 may curve inward.
As described above, the shape of the openings 12a may be distorted even when the pattern mask 10 is fixed on the frame 20 and an even tensile force is applied. This may generate errors between an electrode pattern (not shown) of a unit device formed on the substrate and the openings 12a of the mask pattern unit portion 12.
In order to solve the above problems, Korean published Patents No. 2003-0046090 and No. 2003-0093959 disclose a mask frame assembly for depositing a thin film of an organic EL device in which a pattern mask is divided into a plurality of unit pattern masks, and both ends of the divided unit pattern mask are fixed to the frame, and tensile force is applied to the frame.
According to the conventional mask frame assembly, the divided unit pattern mask is welded onto the frame to prevent the opening of the mask pattern unit from being transformed due to the tensile force. However, there are still problems with robustness, and maintaining desired gaps between the adjacent unit pattern masks that are fixed onto the frame.